1. Field of the Invention
This invention relates to a recording liquid to be used for various recording instruments such as writing implements, printers, etc. (hereinafter called an ink), particularly an ink suitable for the ink jet recording system in which recording is effected by ejecting liquid droplets through the orifice of a recording head and also, to a recording method by use thereof.
2. Description of the Related Art
The ink jet recording system has the advantages of generating minimal noise during recording being sufficiently adaptable to color printing, and capability of obtaining recorded images of high resolution at high speed.
In ink jet recording systems, solutions of various water-soluble dyes dissolved in water or mixtures of water and organic solvents have been extensively used as the ink. Such ink is generally required to have the performances as shown below in relation to the recording medium.
(1) No feathering should occur at the printed portion on the recording medium.
(2) The ink should dry rapidly (including drying by absorption) on the recording medium.
(3) The ink should cause not clog of the nozzle of a printer, even if printing may be intermitted indefinitely.
(4) Frequency response for discharging ink in comformity with the printing speed of a printer should be good.
(5) Storage stability of ink should be high.
(6) Safety should for human use be high, etc.
Of these requisite performances, the point which is particularly technically difficult is to accomplish simultaneously the above items (1), (2), (3) and (4).
In order to satisfy the various requisite performances as described above, various studies have been made on colorants such as water-soluble dyes, water and organic solvents as media and additives such as surfactants, etc.
However, in spite of a large number of studies up to date, all of the above requisite performances are not necessarily satisfied, and therefore in order to cover the inferior points of the ink performance at the printing stage, a large number of recording medium called paper for ink jet recording have been proposed.
As described above, use of a specific ink and a paper intended for ink jet recording and adapted for said ink will give substantially satisfactory results with respect to quality of printed letters and drying fixing characteristic of ink. However, when ink jet recording is practiced for papers generally used in business such as copying paper, report paper, bond paper, slip paper, continuous business form paper, high-size paper, low-size paper, plain paper, etc., various problems will ensue (depending on the properties of the paper used) such as delay in fixing and drying, feathering of ink, etc.
For example, an organic solvent such as glycol is often added into an ink for ink jet recording for the purpose of preventing drying, clogging of nozzle, etc. When recording is effected on a plain paper with high size degree with such an ink, unpractically long time is required for drying of ink due to low liquid-absorbing property of these papers. Also, for enhancing ink absorptivity, a surfactant can be added to the ink. However, in this case, although drying speed can be improved, feathering of the printed letters becomes greater, thereby ensuing another problem that no image of high quality can be obtained. It is also proposed to add a strongly alkaline substance in place of a surfactant, but in this case, the image quality, etc., are influenced by the kind of the additive in the paper. For example, no effect can be obtained in neutral papers, etc. Also, such an ink which is strongly alkaline is highly dangerous for use in households or offices.
For example, Japanese Laid-open Patent Publication No. 213067/1983 discloses an ink for ink jet recording containing a dissolving agent for dyes. However, when printing is effected on a plain paper by use of this ink, there are problems such that a long time is required for drying, that printing speed is slow, etc.